First, it's important to note that not everyone thinks that wearing shoes indoors is a faux-pas. Guests in my home are welcome to leave their shoes on, and when I'm the guest I follow these three simple guidelines:
1. Always wipe your feet on the doormat.
2. Before you step inside scan the front-entry way for signs that others have left their shoes at the door and sneak a peek at your hosts feet.
3. When in doubt, use my favorite question "is this a shoes-on or shoes-off house?"
Need more clues? Carpeted homes usually have sock-footed inhabitants while marble or hardwood floors might be more shoe friendly.
Now, let's say you are hosting a party and you have a strictly shoes-off home. You should absolutely provide alternative footwear for your guests. There will be guests who will not be wearing socks with their shoes and would be barefoot in this situation and may feel awkward or uncomfortable. Think Japanese slippers neatly laid out at the front door welcoming your guests to slip their feet into them. Or, what about providing themed socks? It'd be a nice ice breaker and a fun element to your already great get-together!
Finally, if you let your toes breathe all the time indoors, be sensitive to the fact that some guests might be uncomfortable with that! Rule of thumb: socks. This will invite your guests to be comfortable without being grossed out.
Tell us, what do you do when you are the guest? And when you're hosting, are shoes on or off at your soiree?